Virtual Methods in Creep Crack Growth Predictions in 316H Stainless Steels

2007 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Stainless Steels ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Creep Model ◽  
Elastic Plastic ◽  
Creep Crack ◽  
Plastic Creep ◽  
Plane Strain Crack

The paper discusses numerically based virtual techniques of creep crack growth predictions in a fracture mechanics component. The material properties used are for 316H stainless steels and the constitutive behaviour of the steel is described by a power law creep model. A damage-based approach is used to predict the crack propagation rate in compact tension (C(T)) specimens and the data are correlated against an independently determined C* parameter. Elastic-plastic-creep analyses are performed using two different crack growth criteria to predict crack extension under plane stress and plane strain conditions. The NSW and NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions. The plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model, for values of C* within the limits of the present creep crack growth testing standards. At higher loads and C* values, the plane strain crack growth rates, predicted using an elastic-plastic-creep material response, approach is considered and compared to the plane strain NSW-MOD model.

Modelling Crack Growth in the Life Assessment of Elevated Temperature Components

2007 ◽  
Vol 348-349 ◽  
pp. 709-712
Author(s):  
Kamran M. Nikbin
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Plane Strain ◽  
Elevated Temperatures ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Life Assessment ◽  
Manganese Steel ◽  
Growth Data ◽  
Creep Crack

Modelling of Creep Crack Growth (CCG) using analytical and numerical methods is relevant to life assessment procedures of components operating at elevated temperatures. This paper compares an analytical crack prediction and a numerical based virtual CCG technique used in fracture mechanics components with sample experimental results. Two approaches are presented. First the well developed strain exhaustion model called the NSW and the modified NSW-MOD models which predict plane stress/strain bound crack initiation and growth rates for engineering alloys and the second a damage-based approach used to numerically predict the crack propagation rate in Finite Element models of fracture mechanics specimens. The results from both methods are correlated against an independently determined C* parameter. As an example the NSW and the extended NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions for two steels at Carbon-Manganese steel tested at 360 oC and a weld 316H stainless steel at 550 oC. For values of C* within the limits of the present creep crack growth data presented the plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model.

Modeling and Simulation of Creep Crack Growth in High Chromium Steels

2014 ◽  
Author(s):  
Nicola Bonora ◽  
Luca Esposito ◽  
Simone Dichiaro ◽  
Paolo Folgarait
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Chromium Steel ◽  
Creep Model ◽  
Model Parameters ◽  
Approximate Methods ◽  
High Chromium ◽  
Creep Crack ◽  
Wide Range

Safe and accurate methods to predict creep crack growth (CCG) are required in order to assess the reliability of power generation plants components. With advances in finite element (FE) methods, more complex models incorporating damage can be applied in the study of CCG where simple analytical solutions or approximate methods are no longer applicable. The possibility to accurately simulate CCG depends not only on the damage formulation but also on the creep model since stress relaxation, occurring in the near tip region, controls the resulting creep rate and, therefore, crack initiation and growth. In this perspective, primary and tertiary creep regimes, usually neglected in simplified creep models, plays a relevant role and need to be taken into account. In this paper, an advanced multiaxial creep model [1], which incorporates damage effects, has been used to predict CCG in P91 high chromium steel. The model parameters have been determined based on uniaxial and multiaxial (round notched bar) creep data over a wide range of stress and temperature. Successively, the creep crack growth in standard compact tension sample was predicted and compared with available experimental data.

Elastic Follow-Up Factors to Estimate C(t) Under Secondary Loading

2012 ◽  
Author(s):  
Kuk-Hee Lee ◽  
Yun-Jae Kim ◽  
Robert A. Ainsworth ◽  
David Dean
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Transient Creep ◽  
Independent Method ◽  
Finite Element Analyses ◽  
Creep Crack ◽  
Reference Stress ◽  
Growth Increase ◽  
Plastic Creep

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.

Computational Modelling of High Temperature Steady State Crack Growth Using a Damage-Based Approach

2003 ◽  
Author(s):  
Masataka Yatomi ◽  
Noel P. O’Dowd ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Computational Study ◽  
Creep Crack Growth ◽  
Computational Modelling ◽  
Crack Tip ◽  
Creep Damage ◽  
Creep Model ◽  
Manganese Steel

In this work a computational study of creep crack growth in a carbon manganese steel is presented. The constitutive behaviour of the steel is described by a power law creep model and the accumulation of creep damage is accounted for through the use of a well-established model for void growth in creeping materials. Two dimensional finite element analyses have been performed for a compact tension specimen and it has been found that the predicted crack growth rate under plane strain conditions approaches that under plane stress conditions at high C* levels. Furthermore it has been shown, both experimentally and numerically, that an increase in test temperature causes the convergence of the cracking rate to occur at higher values of C*. This trend may be explained by the influence of crack-tip plasticity, which reduces the relative difference in constraint between plane stress and plane strain conditions. The constraint effect has been quantified through the use of a two-parameter characterisation of the crack tip fields under creep conditions.

Assessment of Fully Plastic J and C*-Integral Solutions for Application to Elastic-Plastic Fracture and Creep Crack Growth

1993 ◽  
Vol 115 (3) ◽  
pp. 228-234 ◽  
Author(s):  
D. R. Lee ◽  
J. M. Bloom
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Driving Force ◽  
Creep Crack Growth ◽  
J Integral ◽  
Finite Element Program ◽  
Hardening Material ◽  
Crack Driving Force ◽  
Elastic Plastic ◽  
Creep Crack

A critical part of the assessment of defects in power plant components, both fossil and nuclear, is the knowledge of the crack driving force (K1, J, or C*). While the determination of the crack driving force is possible using finite element analyses, crack growth analyses using finite element methods can be expensive. Based on work by Il’yushin, it has been shown that for a power law hardening material, the fully plastic portion of the J-integral (or the C*-integral) is directly related to an h1 calibration function. The value of h1 is a function of the geometry and hardening exponent. The finite element program ABAQUS was used to evaluate the fully plastic J-integral and determine the h1 functions for various geometries. The Ramberg-Osgood deformation theory plasticity model, which may be used with the J-integral evaluation capability, allows the evaluation of fully plastic J solutions. Once it was established that the grid used to generate the h1 functions was adequate (based on the more recent work of Shih and Goan), additional runs were made of other configurations given in the EPRI Elastic-Plastic Fracture Handbook. Differences as great as 55 percent were found when compared to results given in the Handbook (single-edge crack plate under tension and plane stress with a/b = 0.5). Effects of errors in h1 on predicted failure load and creep crack growth are discussed.

scholarly journals Finite element simulation of creep crack growth using combined plastic-creep damage model

2016 ◽  
Vol 2 ◽  
pp. 825-831 ◽  
Author(s):  
Dong-Jun Kim ◽  
Kyung-Dong Bae ◽  
Han-Sang Lee ◽  
Yun-Jae Kim ◽  
Goon-Cherl Park
Keyword(s):  
Finite Element ◽  
Finite Element Simulation ◽  
Crack Growth ◽  
Damage Model ◽  
Creep Crack Growth ◽  
Creep Damage ◽  
Creep Crack ◽  
Element Simulation ◽  
Creep Damage Model ◽  
Plastic Creep

Numerical Prediction of Constraint Effect of Creep Crack Growth

2009 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Creep Crack Growth ◽  
Constraint Effect ◽  
Three Point Bending ◽  
Creep Crack ◽  
Reference Stress ◽  
Edge Notch ◽  
Stress And Strain Rate

This paper presents the effect of constraint on creep crack growth (CCG) using FE analysis based on the stress and strain rate state at the crack tip. The comparison is made by modelling C(T) specimen tests under plane stress and plane strain conditions using creep properties of three different steels (C-Mn steel, P91 steel, and 316H austenitic steel). In addition, in order to examine the constraint effect on CCG due to geometry single edge notch specimen (SENT), centre cracked tension specimen (CCT) and three point bending (3PB) specimen have also been analysed. In all cases it is found that when the reference stress under plane strain conditions is higher than the yield stress, there is little difference between CCG rates under plane stress and plane strain.

Evaluation of Constraint Effect on Creep Crack Growth by Advanced Creep Modeling and Damage Mechanics

2014 ◽  
Author(s):  
Simone Dichiaro ◽  
Luca Esposito ◽  
Nicola Bonora
Keyword(s):  
Numerical Simulation ◽  
Creep Rate ◽  
Crack Growth ◽  
Damage Mechanics ◽  
Crack Depth ◽  
Creep Crack Growth ◽  
Creep Model ◽  
Secondary Creep ◽  
Creep Stage ◽  
Creep Crack

Effects of constraint induced by crack depth and sample geometry on creep crack behavior of high chromium steels was investigated by numerical simulation. An advanced mechanism-based creep model formulation, which accounts for primary and secondary creep stage was used. Here, the transient creep rate is modeled considering the evolution of the internal stress with the activation energy while the steady state creep rate is modelled considering both diffusional and dislocation creep mechanisms. This formulation allows one to predict accurately creep strain accumulation over a wide range of stress and temperature. Model parameters were identified on constant load creep tests and their transferability to the multiaxial state of stress was verified comparing predicted creep life with data obtained on notched bar samples. Continuum damage mechanics was used to predict the occurrence of tertiary creep stage and crack advance. To this purpose, a non-linear damage law, as proposed in Bonora and Esposito [1] was used. The effect of the geometry constrain on creep crack growth was investigated in different sample geometries (C(T), SEN(T), SEN(B), DEN(T) and CCP(T)) for a given crack depth values, and the same biaxiality ratio for SEN(T), SEN(B) and DEN(T). Numerical simulation results were validated by comparison with available experimental data for P91 steels.

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